Your Assignment –
You will be setting up several fly crosses, comparing offspring ratios, and determining the mode of inheritance of those genes. We will be using mutants in the white gene and in the miniature gene for this lab. The white gene and the miniature gene are both located on the X chromosome. Follow the instructions below, and answer all questions.
Part I
Cross #1:
Select a female fly with the White Eye Color trait, and mate her to a male fly with the Miniature Wing Size trait.
Q1. What are the phenotypes of the offspring from this cross?
Q2. How many of each phenotype are there? You may find it helpful to answer this question by selecting the “Analyze” tab, and checking the box labeled “Ignore sex of flies,” as shown in the image on the previous page.
Cross #2:
Select the female offspring of cross #1, and mate her to a male fly showing both the White Eye Color trait and the Miniature Wing Size trait.
Q3. What are the phenotypes of the offspring from this cross?
Q4. How many of each phenotype are there?
Q5. Assume these genes are inherited through simple Mendelian inheritance. Set up a Punnett’s Square of cross #2. Do the Punnett’s Square results match the results you observe? Explain why or why not.
Q6. Write the genotypes of each of the parents and offspring in crosses #1 and #2. Remember, these genes are on the X chromosome.
Q7. Are the mutant alleles in the female parent in cross #2 in cis or in trans? Draw a diagram of the arrangement of her alleles on both of her X chromosomes.
Q8. For each gene, which alleles are dominant and negative?
Q9. Consider your answer to Q8. What is the name for the specific type of cross you set up for cross #2?
Q11. Propose a non-Mendelian mode of inheritance for the white and miniature genes.
Q12. How far apart on the X chromosome are the white and miniature genes? You must show all work to receive any credit for this question.
Part II
Repeat crosses #1 and #2 using either one of the two genes listed above and the Yellow allele of the Body Color trait. Then answer questions #6 and #12 for these new crosses.
